Human Immunodeficiency Virus (“HIV”), an approximately 10-kb, enveloped, single-stranded RNA retrovirus, is the causative agent of Acquired Immunodeficiency Syndrome (“AIDS”). As the HIV epidemic continues to spread world-wide, the need for effective HIV detection methods remains paramount. Early detection of HIV infection is critical for preventing the spread of the virus and concomitant disease, and for determining effective treatments and therapies. However, a key obstacle to HIV detection and treatment has been—and remains to be—the incredible variability of HIV types, and the extent and swiftness of HIV mutation (Wain-Hobson in The Evolutionary biology of Retroviruses, SSB Morse Ed. Raven Press, NY, pgs 185 209 (1994)).
Molecular characterizations have shown that the HIV virus can be categorized into two broad types. HIV-1, discovered in 1984, is the main cause of AIDS around the world, particularly in the Western Hemisphere and in Europe. HIV-2, discovered two years later in 1986, is noted mainly in western Africa. Both HIV-1 and HIV-2 are additionally categorized into sub-types. For example, HIV-2 is broken down into sub-types A-G; sub-types A and B are considered “epidemic,” while C-G are considered “nonepidemic.” Similarly, molecular characterization of HIV-1 strains from around the world have identified three distinct groups, M, N and O. Group M viruses represent the majority of HIV-1 and based on sequence divergence Group M has been further subdivided into nine different subtypes or clades, termed subtypes A, B, C, D, F, G, H, J, and K (Robertson, D. L. et al. In: Human Retroviruses and AIDS 1999—A Compilation and Analysis of Nucleic Acid and Amino Acid Sequences, Kuiken, C. et. al. Eds., pgs. 492-505 (1999)).
The overall distribution of HIV-1 strains varies considerably in different geographic regions and is undergoing continual change. For example, while subtype B has been predominant in North America and Western Europe (see e.g., McCutchan, F. E., AIDS 14 (suppl 3): S31-S44 (2000)), increasing numbers of non-subtype B infections are being observed in both Europe and the United States.
In addition to the great diversity of types and subtypes, drug-resistant and therapy-resistant mutants have also become prevalent. Due to the extreme mutability of the HIV virus (HIV does not employ a “proof-reading” mechanism during replication), the development of vaccines has been a major challenge, and the use of other drug therapies, such as anti-viral drugs, has been complicated by the rapid evolution of drug resistant strains.
Drug-resistance mutations have been identified in HIV-1 patients who have shown improvement under some type of drug treatment or therapy and have then experienced a “relapse” of HIV-1 viral growth and associated symptoms. Mutations associated with resistance to anti-viral drugs have been found in the gag, pol and env regions of the HIV viral genome, and have been show to affect proteins such as reverse transcriptase, protease, and the GP41 envelope protein (See e.g., Johnson, et al., 2005 Special Contribution—Drug Resistance Mutations in HIV-1, 13:3, 125-131; Gingeras et al., 1991, J. Infect. Dis. 164(6):1066-1074; Richman et al., 1991, J. Infect. Dis. 164(6):1075-1081; Schinazi et al., 1993, Antimicrob. Agents Chemother. 37(4):875-881; Najera et al., 1994, AIDS Res. Hum. Retroviruses 10(1 1):1479-1488; Eastman et al., 1995, J. AIDS Hum. Retrovirol. 9(3):264-273; Frenkel et al., 1995, J. Clin. Microbiol. 33(2):342-347; Shiras et al., 1995, Proc. Natl. Acad. Sci. USA 92(6):2398-2402; Leal et al., 1996, Eur. J. Clin. Invest. 26(6):476-480; Cleland et al., 1996, J. AIDS Hum. Retrovirol. 12(1):6-18; Schmit et al., 1996, AIDS 10(9):995-999; Vasudevechari et al., 1996, Antimicrob. Agents Chemother. 40(11):2535-2541; Winslow et al., 1996, AIDS 10(11):1205-1209; Fontenot et al., Virology 190(1):1-10; Cornelissen et al., 1997, J. Virol. 71(9):6348-6358; Ives et al., 1997, J. Antimicrob. Chemother. 39(6):771-779).
Determining whether an HIV-1 infected patient is carrying drug-resistant viral strains may be critical for proper treatment and therapy. For example, a clinician may be able to decide whether to begin or maintain a particular antiretroviral therapy. Further, continued testing of patients for drug-resistant HIV mutants during treatment may be used to detect the emergence of a drug-resistant virus, thereby allowing the clinician to alter the therapy to something that may prove more effective. Thus, there is a need in the art for assays that provide information related to HIV drug-resistance.